Mixed Metal Oxide Catalyst useful for Paraffin Dehydrogenation

ABSTRACT

The invention relates to a catalyst composition suitable for the dehydrogenation of paraffins having 2-8 carbon atoms comprising zinc oxide and titanium dioxide, optionally further comprising oxides of cerium (Ce), dysprosium (Dy), erbium (Er), europium (Eu), gadolinium (Gd), lanthanum (La), neodymium (Nd), praseodymium (Pr), samarium (Sm), terbium (Tb), ytterbium (Yb), yttrium (Y), tungsten (W) and Zirconium (Zr) or mixtures thereof, wherein said catalyst composition is substantially free of chromium and platinum. The catalysts possess unique combinations of activity, selectivity, and stability. Methods for preparing improved dehydrogenation catalysts and a process for dehydrogenating paraffins having 2-8 carbon atoms, comprising contacting the mixed metal oxide catalyst with paraffins are also described. The catalyst may also be disposed on a porous support in an attrition-resistant form and used in a fluidized bed reactor.

RELATED APPLICATIONS

This application claims the priority benefit of U.S. Provisional PatentApplication Ser. No. 62/739,137 filed 28 Sep. 2018 and U.S. ProvisionalPatent Application Ser. No. 62/849,730 filed 17 May 2019.

BACKGROUND

The US is currently undergoing a quiet revolution in fossil energy.Recent technological advances, specifically the confluence of horizontaldrilling and hydraulic fracturing, have enabled vast gas reserves lockedin shale formations to be cost effectively tapped for the first time. Anestimated 2 quadrillion cubic feet of natural gas is held in theseunconventional reserves in the US, enough to supply the nation's needsfor many decades.

The ability to access these resources has led to a sudden decoupling ofthe traditional link between petroleum and natural gas prices. Domesticnatural gas prices have fallen to historically low levels as a result ofthe introduction of 4.5 trillion cubic feet per year of shale gas,accounting for 20% of the nation's total gas supply.

The abundance of cheap propane, ethane, and methane from shale gas andstranded gas will facilitate cost-competitive paths in the production ofcommodity chemicals such as light olefins. In particular, the on-purposeproduction of propylene has grown as more steam crackers shift fromnaphtha feed to lighter shale condensates. This is especially true inthe United States, where shale gas exploitation has grown exponentially,amplifying the issue of supply due to the strong growth in propylenedemand compared with that of ethylene. Steam cracker units cannot fillthis gap due to the low propylene/ethylene ratio. In this respect, otherproduction routes could be profiled as an interesting alternative toovercome this issue.

The shift from naphtha toward light feeds that are derived from tightoil, for the production of ethylene in steam crackers, has impacted theglobal propylene and crude C₄ production capacity. Therefore, routes forthe production of light olefins have received considerable interest.Catalytic dehydrogenation provides the possibility of high selectivityto a single olefin product—much higher than can be expected from steamcrackers alone. The amount of propylene produced by dehydrogenation was5 million tons in 2017 and is expected to increase.

Two patented industrial processes for the dehydrogenation of alkanes arecurrently in commercial use—namely, the Oleflex process which uses aPlatinum-based catalyst and the Catofin process which uses aChromium-based catalyst. Platinum is expensive and currently sells for$27,000/kg making platinum-based dehydrogenation processes veryexpensive. Chromium-based catalysts are comparatively cheaper. However,chromium is a known carcinogen. The object of the present invention isto provide an improved mixed-metal oxide catalyst for thedehydrogenation of paraffins which is essentially free of eitherPlatinum or Chromium. Compared to metallic platinum and chromium oxide,zinc oxide (ZnO) is an inexpensive and low-toxic alternative fordehydrogenation of propane. Zinc has been shown to activate propanethrough dissociative adsorption over zinc oxide species. For instance,U.S. Pat. No. 2,279,198 describes an active, stable and regenerablecatalytic system consisting of zinc oxide along with other metal oxidesand promoters for the dehydrogenation of alkanes and other organiccompounds. Isobutane conversion as high as 26.4% has been reported at510° C.

Successively precipitated ZnO over zirconium oxide was shown to beactive and stable for the dehydrogenation reaction while addition ofsmall amounts of Li₂O and CaO were shown to further improve the catalystactivity and stability.

Numerous other Zn-based catalysts have been explored for dehydrogenationof hydrocarbons. For example, it is reported that when Zn is introducedinto acidic zeolites like H-ZSMS, the reaction rate for dehydrogenationof paraffins increases²⁻¹³. The Zn²⁺ species are reported to reside inthe cation exchange sites of the zeolite and have a tetrahedralorientation. The main products are aromatic compounds and theselectivity to olefins is usually low (<40%). While the role of Zn inthese reactions is greatly debated, it is believed that Zn carries outthe two-fold function of promoting the dehydrogenation of thehydrocarbon as well as depleting the surface hydrogen pool by thecatalytic recombinative desorption of H-atoms and H₂ ¹⁴. Zinc has alsobeen used as a promoter for alkane dehydrogenation catalysts¹⁵⁻²⁰. Forexample, studies in literature have shown that the addition of Zn to Ptor Cr containing catalysts resulted in increasing the alkene selectivityduring alkane dehydrogenation. It is believed that zinc modifies thegeometric and electronic properties of the metallic phase of Pt andstudies showed that the addition of zinc to Pt—Al₂O₃, PtSn—Al₂O₃,¹⁵ andPtSn—MgAl₂O₄ formulations significantly improved their overallperformance for propane dehydrogenation¹⁷. Zinc is known to alloy withplatinum and the formation of the alloy is believed to increase theelectronic density on the metallic Pt which weakens the alkeneadsorption¹⁵ resulting in reduced coke formation and lower associatedby-product gases such as methane and ethane. Zinc was also shown to beeffective in increasing the activity of hematite towards ethylbenzenedehydrogenation²¹. The authors claimed that while zinc oxide by itselfwas inactive for the reaction, it increased the activity of hematitetowards the dehydrogenation by stabilizing the Fe³⁺ species.

Zinc based catalysts have been shown to be active in the oxidativedehydrogenation of hydrocarbons. While it was known that simple ironoxide, α-Fe₂O₃ catalyzes a rather selective production of butadiene viathe oxidative dehydrogenation of butenes and in some cases n-butane,Rennard and Kehl showed that addition of zinc oxide to iron oxide leadsto the formation of ZnFe₂O₄ which further increases the selectivity tobutadiene under identical conditions²². For example, the selectivitiesfor butadiene on Fe₂O₃ were 83% at 325° C. and 43% at 375° C., while onZnFe₂O₄ they were 89% at 325° C. and 88% at 375° C. Comparison of theseresults with those on iron oxide suggests that zinc ferrite is a moreselective oxidation catalyst because it has a higher density ofselective oxidation sites and a lower density of combustion sites, andbecause its combustion sites are less active than those on ironoxide²²⁻²⁴. Numerous methods of synthesis with and without the presenceof promoters have been described in literature (U.S. Pat. Nos.3,743,683, 3,951,869). For example, it is reported that when a zincferrite catalyst doped with chromium or aluminum was used, catalyticactivity towards dehydrogenation was increased²⁵.

Zinc has been used as a support for the dehydrogenation of loweralkanes. Zinc aluminate has been used as a catalyst support due to itslow specific surface area and high hydrothermal stability26-28. U.S.Pat. Nos. 5,344,805; 5,430,220; and EP 0557982A2 describe a process fordehydrogenating at least one alkane comprising 2 to 8 carbon atoms to analkene in the presence of steam and a catalyst composition comprisingzinc aluminate and platinum. The addition of zinc oxide to alumina for aPt based catalyst was shown to increase the rate of dehydrogenation aswell as the selectivity of alkene as a result of the suppression of thedecomposition reaction and coke formation²⁹. However, zinc aluminates bythemselves are inactive as dehydrogenation catalysts. They require anadditional metal like platinum as part of the catalyst composition to beeffective.

Pt and Cr free catalysts have been synthesized via a coprecipitationmethod using nitrates of various metals and were shown to be active andselective for the dehydrogenation of isobutane to isobutene (U.S. Pat.No. 9,713,804B2, WO2013091822A1). The most active, selective and stablecomposition consisted of mixed Zn, Mn and Al oxides. Numerous promoters,selected from alkali metals (K, Cs), non-metals (Si) and transitionmetals (Fe, Cr, Cu, Zr, Ce etc.) were used to promote these catalystswith varying degrees of success. These catalysts showed high activity(up to 56% conversion of isobutane) and high selectivity (up to 96%) toisobutene at 550° C. and a space velocity of 0.6 hr-1. These catalystsalso showed reasonable stability with just a moderate drop in activityfor up to 500 reaction-regeneration cycles. However, no data wasprovided for the application of this catalyst to other hydrocarbons likeethane and propane. Zinc titanate is reported to be active in thedehydrogenation of alkanes. Zinc titanate was first reported to beactive for the dehydrogenation of isobutane by Phillips Petroleumresulting in a modest isobutene yield. Later, it was also applied forthe dehydrogenation of a number of paraffins, olefins, cycloaliphaticsand alkyl aromatic compounds having from 2 to 12 carbon atoms permolecule as described in patents U.S. Pat. Nos. 4,368,344A, 4,389,337A,4,524,144A, 4,144,277A, 4,394,297A, 4,218,346A,.

U.S. Pat. Nos. 4,228,040A, 4,389,337, 4,463,213, 4,176,140 and 4,327,238show that various promoters, either transition metals, alkali metals oralkaline earth metals can be used with the zinc titanate of U.S. Pat.No. 4,144,277 to improve the yield of unsaturated compounds. Thecatalyst was usually prepared by intimately mixing suitable proportionsof zinc oxide and titanium dioxide wherein the atomic ratio of zinc totitanium was usually close to 2:1 and calcining the resulting mixture inair at a temperature in the range of 675° to 975° C. The catalysts werealso prepared by coprecipitation of a mixture of aqueous solutions of azinc compound and a titanium compound. The aqueous solutions were mixedtogether and the hydroxides were precipitated by the addition ofammonium hydroxide. The precipitate was then washed, dried and calcined.Promoters were either added during the coprecipitation with zinc andtitanium compounds or the zinc and titanium were first coprecipitatedand the coprecipitate was then impregnated with a suitable amount of thepromoter. These patents report that the most active zinc orthotitanatecatalyst was obtained when the titania particle size was small or whenthe catalysts were prepared by coprecipitation.

High yields of the unsaturated compounds were reported. Ethylene yieldof 33% from ethane at 666° C. (U.S. Pat. No. 4,389,337), propylene yieldof 67.75% at 621° C. (U.S. Pat. No. 4,228,040) and isobutene yield of54% at 625° C. (U.S. Pat. No. 4,463,213) are reported to list a few.Usually, the reaction time was 3 minutes followed by a nitrogen purgefor 3 minutes and then regeneration in air for 6 minutes. It ismentioned that the catalysts are subjected to numerousreaction-regeneration cycles. However, since no stability data ispresented it is not clear whether the catalyst performance changes overthe course of time with successive reaction-regeneration cycles. Itshould also be noted that the dehydrogenation tests were carried out inthe presence of nitrogen as a diluent.

Lysova et al. studied the effect of the chemical composition of theZnO—TiO₂ catalytic system on its phase composition and catalyticproperties in the oxidative and nonoxidative dehydrogenation ofisobutane³⁰. It was found that samples with an atomic ratio of zinc totitanium≥2 exhibited the highest selectivity with high specificactivity. It was reported that ZnO—TiO₂ system was active and selectivein ODH of isobutane at 570° C., the maximum yield of isobutene being54%.

Chen et al. prepared thin films (80-100 nm) of zinc titanate with Zn/Tiratios between 0.5 and 2.7 on 200 Si(100) wafers via the metalloorganicdecomposition (MOD) technique and investigated them for alkanedehydrogenation reactions³¹. Catalytic testing of these films forisobutane dehydrogenation showed a clear correlation between thestructure and the catalytic performance which depended on the filmstoichiometry. Zinc titanate phases, with a Zn/Ti ratio close to 2 had acubic crystal structure and were found to be active for dehydrogenationwhile the other phases were not. The isobutane conversion was 2% at 823K and 8 mol % at 923 K, with a selectivity of 90% to isobutene.

Zn/SiO₂—Schweitzer et al. tested a Zn/SiO₂ catalyst for thedehydrogenation of propane³². The reaction was run under differentialconditions (target conversion of less than 10%). Propylene selectivitywas reported to be >95% at 550 C and the catalyst lost only 50% of itsactivity in 12 hours. In this catalyst, the Zn²⁺ center is coordinatedwith three O centers of the SiO2 surface and is believed to be theactive species. It was shown through various computational andcharacterization methods that the active site catalyzes the heterolyticcleavage of the C—H bonds of propane and the undesired C—C cleavagereactions are shown to be kinetically less favorable resulting in ahigher propylene selectivity. However, the dehydrogenation reaction wasrun with an extremely dilute 3% propane in Argon reaction mixture.Additionally, while it was mentioned that conversion reached 20% at 550°C., no time on stream data is provided for high conversions.

Sun et al. report that Zn—Nb—O oxides are active and selective in thecatalytic dehydrogenation of propane to propylene³³. A propylene yieldof 28.1 wt. % with selectivity of 84% were observed over the catalystwhich was calcined at 600° C. and had a molar ratio of ZnO/Nb₂O₅=3.ZnNb₂O₆ was suggested to be the active site for the dehydrogenationreaction. Temporary, reversible deactivation was observed which wasattributed to the formation of coke while the loss of ZnO speciesleading to the formation of Zn₃Nb₂O₈ phase was suggested to be thereason for the irreversible deactivation of the catalyst.

U.S. Pat. No. 7,087,802, U.S. Published Patent Application No.2016/0074838 and U.S. Pat. No. 6,518,476 describe catalyst systems forthe oxidative and/or non-oxidative dehydrogenation of light alkaneswhere the catalyst consists of a support and an active component. Thesupport is generally a heat-resistant oxide and could be selected fromzirconium dioxide, zinc oxide, aluminum oxide, silicon dioxide, titaniumdioxide, magnesium oxide, lanthanum oxide, cerium oxide and mixturesthereof. The active component could be a precious metal like Pt or Pd orcan be from the other transition, alkali or alkaline earth metal or amixture of the above components. It was also suggested that thedehydrogenation catalyst described in these patents can be used in theform of a fixed bed in the reactor or in the form of a fluidized bedwith an appropriate shape.

Despite these and other efforts, there remains a need in the industry todevelop cost-effective, environmentally friendly dehydrogenationcatalysts that are commercially viable.

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SUMMARY OF THE INVENTION

In a first aspect, the invention provides a mixed metal oxide catalystsuitable for the dehydrogenation of paraffins having 2-8 carbon atomswith a catalyst composition of the general formula (AC) (CS) (ST)wherein

-   -   a) AC represents oxides of Transition Metals selected from the        group of copper (Cu), iron (Fe), manganese (Mn), niobium (Nb)        and zinc (Zn) or mixtures thereof,    -   b) CS represents oxides of aluminum (Al), silicon (Si), titanium        (Ti) and zirconium (Zr) or mixtures thereof,    -   c) ST represents oxides of Rare Earth metals selected from the        group of cerium (Ce), dysprosium (Dy), erbium (Er), europium        (Eu), gadolinium (Gd), lanthanum (La), neodymium (Nd),        praseodymium (Pr), samarium (Sm), terbium (Tb), ytterbium (Yb),        and yttrium (Y) or mixtures thereof, and    -   characterizable by an Activity Parameter>1500, Selectivity        Parameter<0.2 and a stability parameter<0.005 using a test where        the mixed metal oxide catalyst is loaded in a fixed-bed reactor        such that the 50>dT/dP>10 (diameter of tube to diameter of        catalyst particles) and 200>L/dP>50 (length of catalyst bed to        diameter of catalyst particles) and 2>dP>0.5 mm exposed to a        feed stream of propane at a temperature of 625° C., atmospheric        pressure and a feed rate of 1 hr⁻¹ or 2 hr⁻¹ weight hourly space        velocity.

In a related aspect, the invention provides a mixed-metal oxide catalystsuitable for the dehydrogenation of paraffins having 2-8 carbon atomscomprising oxides of Transition Metals selected from the group of copper(Cu), iron (Fe), manganese (Mn), niobium (Nb) and zinc (Zn) as theactive catalytic species wherein the active species makes up 0.1 to 20wt % of the total weight of the catalyst, preferably 0.1 to 7.5 wt %,oxides of aluminum (Al), silicon (Si), titanium (Ti) and zirconium (Zr)or mixtures thereof as the catalyst support wherein the catalyst supportmakes up 10 to 90 wt % of the total weight of the catalyst, preferably50 to 80 wt % and oxides of Rare Earth metals as catalyst stabilizersselected from the group of cerium (Ce), dysprosium (Dy), erbium (Er),europium (Eu), gadolinium (Gd), lanthanum (La), neodymium (Nd),praseodymium (Pr), samarium (Sm), terbium (Tb), ytterbium (Yb), andyttrium (Y) wherein the catalyst stabilizer makes up 0.1 to 20 wt % ofthe total weight of the catalyst, preferably 1 to 10 wt % andcharacterizable by

-   -   a) Activity Parameter>1500,    -   b) Selectivity Parameter<0.2, and    -   c) Stability parameter<0.005    -   measured using a test where the metal oxide catalyst is loaded        in a fixed-bed reactor such that the 50>d_(T)/d_(p)>10 (diameter        of tube to diameter of catalyst particles) and 200>L/d_(P)>50        (length of catalyst bed to diameter of catalyst particles) and        2>d_(P)>0.5 mm exposed to a feed stream comprising of propane at        a temperature of 625° C., atmospheric pressure and a feed rate        of 1 hr⁻¹ weight hourly space velocity.

In a further aspect, the invention provides mixed metal oxide catalystsuitable for the dehydrogenation of paraffins having 2-8 carbon atomswith a catalyst composition of the general formula (AC) (CS) (ST)wherein

-   -   a) AC represents oxides of Transition Metals selected from the        group of copper (Cu), iron (Fe), manganese (Mn), niobium (Nb)        and zinc (Zn) or mixtures thereof,    -   b) CS represents oxides of aluminum (Al), silicon (Si), and        titanium (Ti) or mixtures thereof,    -   c) ST represents oxides of Rare Earth metals selected from the        group of cerium (Ce), dysprosium (Dy), erbium (Er), europium        (Eu), gadolinium (Gd), lanthanum (La), neodymium (Nd),        praseodymium (Pr), samarium (Sm), terbium (Tb), ytterbium (Yb),        yttrium (Y), tungsten (W), zirconium (Zr), or mixtures thereof,        and    -   characterizable by a Activity Parameter>1500, Selectivity        Parameter<0.2 and a stability parameter<0.005 using a test where        the mixed metal oxide catalyst is loaded in a fixed-bed reactor        such that the 50>dT/dP>10 (diameter of tube to diameter of        catalyst particles) and 200>L/dP>50 (length of catalyst bed to        diameter of catalyst particles) and 2>dP>0.5 mm exposed to a        feed stream of propane at a temperature of 625° C., atmospheric        pressure and a feed rate of 1 hr⁻¹ or 2 hr⁻¹ weight hourly space        velocity.

In another aspect, the invention provides mixed metal oxide catalystcomprising a catalyst composition of the general formula (AC) (CS) (ST)(MS) wherein

-   -   a) AC (Active Catalyst) represents oxides of Transition Metals        selected from the group of copper (Cu), iron (Fe), manganese        (Mn), niobium (Nb) and zinc (Zn) or mixtures thereof,    -   b) CS (Catalyst Support) represents oxides of aluminum (Al),        silicon (Si), and titanium (Ti) or mixtures thereof,    -   c) ST (Support Stabilizer) represents oxides of metals selected        from the group of cerium (Ce), dysprosium (Dy), erbium (Er),        europium (Eu), gadolinium (Gd), lanthanum (La), neodymium (Nd),        praseodymium (Pr), samarium (Sm), terbium (Tb), ytterbium (Yb),        yttrium (Y) Tungsten (W) and zirconium (Zr) or mixtures thereof,    -   d) MS (Mechanical Stabilizer) represents porous spheres selected        from the group of alumina, silica, titania, zirconia, kaolin,        meta-kaolin, bentonite, attapulgite, or mixtures thereof;    -   and characterizable by a Activity Parameter>1500, Selectivity        Parameter<0.5 and a stability parameter<0.005 using a test where        the mixed metal oxide catalyst is loaded in a fixed-bed reactor        such that the 50>dT/dP>10 (diameter of tube to diameter of        catalyst particles) and 200>L/dP>50 (length of catalyst bed to        diameter of catalyst particles) and 2>dP>0.5 mm exposed to a        feed stream of propane at a temperature of 625° C., atmospheric        pressure and a feed rate of 2 hr⁻¹ weight hourly space velocity.

In a preferred embodiment, the MS (mechanical stabilizer) species makesup 20 to 85 wt % of the total weight of the catalyst.

In order to characterize a catalyst, it is loaded into a fixed bed. Finecatalyst powders can be characterized by the same measurement bypelletizing the fine powder into a size suitable for fixed bed testing.

In a further aspect, the invention provides catalyst compositioncomprising zinc oxide with optional modifiers selected from the group ofCopper, Manganese, and Niobium and a stabilized titania support,comprising: the stabilized titania support stabilized with a stabilizingelement comprising zirconium, tungsten, or a rare earth element orcombinations thereof; and Zn; wherein the catalyst composition from 10to 95 wt % titania, 0.1 to 25 wt % of the stabilizing element(s), 0 to 3wt % of the modifiers; and 0.1 to 10 wt % Zn; and characterizable by anActivity Parameter>1500, Selectivity Parameter<0.2 and a stabilityparameter<0.005 using a test where the mixed metal oxide catalyst isloaded in a fixed-bed reactor such that the 50>dT/dP>10 (diameter oftube to diameter of catalyst particles) and 200>L/dP>50 (length ofcatalyst bed to diameter of catalyst particles) and 2>dP>0.5 mm exposedto a feed stream of propane at a temperature of 625° C., atmosphericpressure and a feed rate of 1 hr⁻¹ (or 2 hr⁻¹) weight hourly spacevelocity.

Since the catalysts cannot be completely distinguished from the priorart based solely on their elemental composition, the measurementdescribed above is needed for a unique characterization of the catalyst.In various embodiments, the catalyst may be further characterized by anyof the compositions or physical characteristics described herein.

In various embodiments, any of the catalysts can be furthercharacterized by one or any combination of the following: comprisingless than 100 ppm or less than 50 ppm by weight of either platinum (Pt)or chromium (Cr); wherein the Brunauer-Emmet-Teller (BET) surfacearea>30 m²/g; wherein the number average particle size of themixed-metal oxide catalyst is in the range of 30-3000 microns; whereinthe Air Jet Index is less than 10 and most preferably less than 5;wherein the active catalyst species makes up 0.1 to 10 wt % of the totalweight of the catalyst; wherein the active catalyst species makes up 0.1to 7.5 wt % of the total weight of the catalyst; wherein the CS(catalyst support) makes up 10 to 95 wt % of the total weight of thecatalyst; wherein the catalyst support makes up 20 to 90 wt % of thetotal weight of the catalyst; wherein the catalyst support makes up 50to 85 wt % of the total weight of the catalyst; wherein the ST (catalyststabilizer) makes up 0.1 to 25 wt % of the total weight of the catalyst;wherein the catalyst stabilizer makes up 1 to 15 wt % of the totalweight of the catalyst; wherein the catalyst stabilizer makes up 1 to 10wt % of the total weight of the catalyst; wherein the catalyst supportcomprises a mesoporous bead and wherein the number average particle sizeof the mesoporous bead is in the range of 30-3000 micrometers.

In another aspect, the invention provides method of synthesizing amixed-metal oxide catalyst suitable for the dehydrogenation of paraffinsby first contacting the catalyst support with a solution comprising asalt solution of a rare earth metal, calcining the catalyst support byheating said catalyst support impregnated with rare earth metals toproduce a stabilized catalyst support, contacting the stabilizedcatalyst support with a salt solution of a transition metal and finallycalcining the catalyst intermediate to produce the final form ofcatalyst wherein the particle diameter of the final catalyst is 30-3000microns.

In another aspect, the invention provides a method of synthesizing thecatalyst support using a sol gel procedure where the organic alkoxide ofthe support or mixtures are first dissolved in an organic solvent, thesolution is hydrolyzed using either a mineral acid or base. Finally, theresultant sol-gel mixture/s is dried and calcined to produce thecatalyst support. The catalyst support is then contacted with a solutioncomprising a salt solution of a rare earth metal, calcining the catalystsupport by heating said catalyst support impregnated with rare earthmetals to produce a stabilized catalyst support. The stabilized catalystsupport is then impregnated with a salt solution of a mixture oftransition metals and finally calcining the catalyst intermediate toproduce the final form of catalyst wherein the particle diameter of thefinal catalyst is 30-3000 microns (μm).

In another aspect, the invention provides a method of synthesizing thecatalyst support using a co-precipitating procedure where the salts ofthe support or mixtures are first dissolved in water, co-precipitatingthe salts from the solution using a precipitating agent. Finally, theresultant precipitate is dried and calcined to produce the catalystsupport. The catalyst support is then contacted with a solutioncomprising a salt solution of a rare earth metal, calcining the catalystsupport by heating said catalyst support impregnated with rare earthmetals to produce a stabilized catalyst support. The stabilized catalystsupport is then impregnated with a salt solution of a mixture oftransition metals and finally calcining the catalyst intermediate toproduce the final form of catalyst wherein the number average particlesize of the final catalyst is 30-3000 microns (μm).

In another embodiment, the catalyst support is first grafted onto amesoporous bead where the pore dimeter of the mesoporous bead is 3-25nanometers. The objective is to provide the catalyst with sufficientmechanical strength required to operate in fluidized bed reactor. Thegrafting of the catalyst support is accomplished by first dissolving theorganic alkoxide of the support or mixtures in an organic solvent,impregnating the pores of the mesoporous beads with the organic alkoxidesolution, drying and calcining the mesoporous beads to produce thegrafted catalyst support. The catalyst support or the final catalyst iscalcined preferably at 550-650° C. for 2-24 hrs in air. The graftedcatalyst support is impregnated with a salt solution of a mixture oftransition metals and finally calcining the catalyst intermediate toproduce the final form of catalyst wherein the particle size of thefinal catalyst is 30-3000 microns.

In another embodiment, the grafting of the catalyst support isaccomplished by first dissolving salts of the support or mixtures inwater, impregnating the pores of the mesoporous beads with the saltsolution, drying and calcining the mesoporous beads to produce thegrafted catalyst support. The catalyst support or the final catalyst iscalcined preferably at 550-650° C. for 2-24 hrs in air. The graftedcatalyst support is impregnated with a salt solution of a mixture oftransition metals and finally calcining the catalyst intermediate toproduce the final form of catalyst wherein the particle size of thefinal catalyst is 30-3000 microns.

In another aspect, the invention provides a method for preparing acatalyst comprising the steps of: a) dissolving salts of activematerial, catalyst support and support stabilizer in a solvent; b)coprecipitating the salts using a precipitating agent; and c) drying andcalcining the resultant precipitate to produce the mixed metal oxidecatalyst.

In another aspect, the invention provides a method for preparing acatalyst comprising the steps of:

-   -   a) providing a salt solution comprising salts of Al, Si, Ti, or        Zr or mixtures thereof dissolved in water;    -   b) impregnating mesoporous beads with the salt solution;    -   c) drying and calcining the mesoporous beads to produce the        grafted catalyst support;    -   d) contacting the catalyst support with a solution comprising a        salt of a rare earth metal or mixtures thereof;    -   followed by addition of rare-earth and transition metals        comprising the steps of    -   e) calcining said catalyst support by heating said catalyst        support impregnated with rare earth metals to produce a        stabilized catalyst support;    -   f) contacting the stabilized catalyst support with a solution        comprising a salt of a transition metal or mixtures thereof to        make a catalyst intermediate; wherein the transition metal is        selected from the group of consisting of: copper (Cu), iron        (Fe), manganese (Mn), niobium (Nb) and zinc (Zn) or mixtures        thereof; and    -   g) calcining the catalyst intermediate to produce the mixed        metal oxide catalyst.

In another aspect, the invention provides a method for preparing acatalyst comprising the steps of:

-   -   a) dissolving organic alkoxides of catalyst support and support        stabilizer in an organic solvent,    -   b) contacting the organic alkoxide solution or mixtures thereof        with porous spheres,    -   c) drying and calcining the porous spheres to produce the        grafted catalyst support,    -   d) contacting the grafted catalyst support with a solution        comprising a salt of active catalyst metal or mixtures thereof,    -   e) calcining the catalyst intermediate to produce the mixed        metal oxide catalyst.

In another aspect, the invention provides a method for preparing acatalyst comprising the steps of:

-   -   a) providing a salt solution comprising salts of catalyst        support and support stabilizer dissolved in a solvent;    -   b) impregnating porous spheres with the salt solution;    -   c) drying and calcining the porous spheres to produce the        grafted catalyst support;    -   d) contacting the grafted catalyst support with a solution        comprising a salt of a transition metal or mixtures thereof to        make a catalyst intermediate; wherein the transition metal is        selected from the group of consisting of: copper (Cu), iron        (Fe), manganese (Mn), niobium (Nb) and zinc (Zn) or mixtures        thereof; and    -   e) calcining the catalyst intermediate to produce the mixed        metal oxide catalyst.

In another aspect, the invention provides a method for preparing acatalyst comprising the steps of:

-   -   a) providing a salt solution comprising salts of active        catalyst, catalyst support, and support stabilizer dissolved in        a solvent;    -   b) impregnating porous spheres with the salt solution; and    -   c) drying and calcining the porous spheres to produce the mixed        metal oxide catalyst.

In another aspect, the invention provides a method for preparing acatalyst composition comprising the steps of:

-   -   a) optionally, contacting the catalyst support with a solution        comprising a salt of a rare earth metal or mixtures thereof to        produce an impregnated catalyst support;    -   b) optionally, calcining said catalyst support by heating said        catalyst support impregnated with the rare earth metals to        produce a stabilized catalyst support;    -   c) contacting the stabilized catalyst support with a solution        comprising a salt of the transition metal or mixtures thereof,    -   d) calcining the catalyst intermediate to produce the mixed        metal oxide catalyst.

In some preferred embodiments, the catalyst support is synthesized usinga sol gel procedure comprising the steps of a) dissolving organicalkoxides of catalyst support and support stabilizer in an organicsolvent; b) hydrolyzing the organic alkoxide solution, preferably in thepresence of an acid or base catalyst, to produce a gel; and c) dryingand calcining the resultant gel to produce the catalyst support.

In some embodiments, the catalyst support is synthesized using inorganicsalts comprising the steps of: a) dissolving salts of catalyst supportand support stabilizer in a solvent; b) coprecipitating the salts usinga precipitating agent; and c) drying and calcining the resultantprecipitate to produce the catalyst support.

In another aspect, the invention provides a method for preparing acatalyst comprising the steps of:

-   -   a) dissolving the organic alkoxide of the support or mixtures        thereof in an organic solvent    -   b) contacting the organic alkoxide solution or mixtures thereof        with mesoporous beads    -   c) drying and calcining the mesoporous beads to produce the        grafted catalyst support    -   d) contacting the catalyst support with a solution comprising a        salt of a rare earth metal or mixtures thereof;    -   followed by addition of rare-earth and transition metals        comprising the steps of    -   e) calcining said catalyst support by heating said catalyst        support impregnated with rare earth metals to produce a        stabilized catalyst support;    -   f) contacting the stabilized catalyst support with a solution        comprising a salt of a transition metal or mixtures thereof; and    -   g) calcining the catalyst intermediate to produce the mixed        metal oxide catalyst.

In another aspect, the invention provides a method for preparing acatalyst comprising the steps of: a) providing a salt solutioncomprising salts of Al, Si, Ti, or Zr or mixtures thereof dissolved inwater; b) impregnating mesoporous beads with the salt solution; c)drying and calcining the mesoporous beads to produce the graftedcatalyst support; d) contacting the catalyst support with a solutioncomprising a salt of a rare earth metal or mixtures thereof; followed byaddition of rare-earth and transition metals comprising the steps of: e)calcining said catalyst support by heating said catalyst supportimpregnated with rare earth metals to produce a stabilized catalystsupport; f) contacting the stabilized catalyst support with a solutioncomprising a salt of a transition metal or mixtures thereof to make acatalyst intermediate; wherein the transition metal is selected from thegroup of consisting of: copper (Cu), iron (Fe), manganese (Mn), niobium(Nb) and zinc (Zn) or mixtures thereof; and g) calcining the catalystintermediate to produce the mixed metal oxide catalyst.

In any of the methods of making the catalyst support or the mixed metaloxide catalyst, in some embodiments, the support or catalyst be calcinedat 500-1,100° C., preferably at 550-800° C. and most preferably at550-650° C. for 2-6 hrs in an oxygen containing atmosphere, preferablyair. In some embodiments, the volume average pore diameter of themesoporous bead is in the range of 3-500 nm or 3-25 nm.

The invention also includes processes of dehydrogenating a paraffin(preferably propane or isobutane), comprising contacting the paraffinwith any of catalysts described herein in a reaction chamber underconditions sufficient to dehydrogenate the paraffin and resulting in anolefin. The sufficient conditions are conventional conditions fordehydrogenation or identified with no more than routine experimentation.

In a further aspect, the invention provides a process for continuousdehydrogenating of paraffins having 2-8 carbon atoms, preferably propaneor isobutane, comprising: contacting said paraffins with any of thecatalyst compositions described herein at a reaction temperature of500-800° C., a space velocity of 0.1-5 hr⁻¹ or 0.1-1 hr⁻¹ and a pressureof 0.01-0.2 MPa for a reaction period in the range of 0.05 seconds to 10minutes; regenerating the said catalyst with an oxygen-containing gaswherein said catalyst regeneration is performed at a reactiontemperature of 500-800° C., a pressure of 0.01-0.2 MPa and aregeneration period ranging from 0.05 seconds to 10 minutes. In somepreferred embodiments, the contacting step is carried out in a fluidizedbed reactor or a fixed-bed swing reactor.

Another aspect of the invention provides a continuous method fordehydrogenating paraffins having 2-8 carbon atoms wherein the process isperformed at a reaction temperature of 500-800° C., a space velocity of0.1-1 h⁻¹ and a pressure of 0.01-0.2 MPa. The fluidized bed version ofthe method is shown in FIG. 1. In this method, the paraffin feedstock 1is contacted with the catalyst under dehydrogenation conditions for areaction period in the range of about 0.05 second to 10 minutes inReactor/Riser A. Following the reaction period, the Reactor outletstream 2 containing catalyst and product gas flows to theCyclone/Disengager B in which the catalyst is separated from the ProductStream 3. The Separated Catalyst stream 4 is thereafter regenerated inRegenerator C by contacting said catalyst with Combustion Air 5. Thecatalyst regeneration is performed at a temperature of 500-800° C., apressure of 0.01-0.2 MPa and a regeneration period ranging from about0.05 seconds to 10 minutes and producing Flue Gas stream 6 andRegenerated Catalyst stream 7, which is routed again to theReactor/Riser A. The process can be carried out using a Reactor/Riser Aconfigured as a fluidized bed reactor or as a fixed-bed swing reactor.

In some preferred embodiments, the invention provides advantages suchas: the product of the catalyst activity and catalyst selectivityexceeding 0.1 ton of product per hour per ton of catalyst; and theoverall catalyst consumption does not exceed 1 kg of catalyst per ton ofproduct. None of the prior art catalysts listed in the prior art meetthese three characteristics simultaneously.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates a continuous method for dehydrogenatingparaffins in a fluidized bed reactor.

FIG. 2 shows an x-ray diffraction spectrum (XRD) of a ZrO₂ doped TiO₂support; sample AI in the Examples section.

FIG. 3 shows an XRD of commercial ZnO.TiO₂ sample, AK.

GLOSSARY

Arrhenius Activation Energy (E): The Arrhenius equation gives thequantitative basis of the relationship between the activation energy andthe rate at which a reaction proceeds. Arrhenius activation energy termfrom the Arrhenius equation is as an experimentally determined parameterthat indicates the sensitivity of the reaction rate to temperature. Fromthe equation, the activation energy can be found through the relation

k=k ₀ e ^(−E/RT)

Where k is the rate constant of a reaction at temperature T, k₀ ispre-exponential factor, E is activation energy for the reaction, R theuniversal gas constant, T the reaction temperature (in Kelvin). k iscalculated from conversion (x) and residence time (t) as follows

k=−ln(1−x)/τ

Activity Parameter—The catalyst activity is quantified by the activityparameter which is the pre-exponential factor in the Arrhenius equationk₀ for the dehydrogenation reaction, an empirical relationship betweentemperature and rate coefficient using a value of 81.7 kJ/mole for E theActivation Energy for the dehydrogenation reaction using for Titaniabased catalyst.

Selectivity Parameter—Since selectivity of propylene varies with propaneconversion, a method is required to compare selectivity obtained bydifferent catalysts under various conversions. Selectivity parameter iscalculated from the ratio of the rate constant of the propylene crackingreaction (k_(c)) measured in the absence of any diluent such asnitrogen, steam, helium or hydrogen to the rate constant of the propanedehydrogenation reaction (k_(d)) and remains constant irrespective ofthe propane conversion. A catalyst producing propylene with a highselectivity will have a selectivity parameter<0.2.

The selectivity parameter (=k_(C)/k_(D)) is calculated from propaneconversion (x) and propylene yield (y) by solving the equations shownbelow:

k _(D)=−ln(1−x)τ

y=[k _(D)/(k _(C) −k _(D))][e ^((−kDτ)) −e ^((kCτ))]

Stability Parameter—The loss of catalyst activity with time isquantified by the stability parameter which measures the rate of changeof catalyst activity with time. A catalyst with high stability will havea low stability parameter value<0.005.

Stability Parameter=|(k _(Dt) −k _(D0))|/(k _(D0) *t)

Where k_(Dt) is the rate constant of dehydrogenation of propane attime=t, k_(D0) is the rate constant of dehydrogenation of propane attime=0 and t is the time on stream

For instance, at a reaction temperature of T=625° C. (898 K) andresidence time τ=1 second, for a propane conversion of x=46% andpropylene yield of y=42%

-   -   Activity Parameter=35,028    -   Selectivity Parameter=0.23

Characterization of the catalyst is conducted in the absence of adiluent gas such as nitrogen, hydrogen, steam or helium.

Attrition Index: The attrition resistance of catalysts used in fluidizedreactor systems are characterized by the Attrition Index determined byASTM tests such as AJI—Air Jet Index which is the percent attrition lossat 5 hours (ASTM D5757—Standard Test Method for Determination ofAttrition of FCC Catalysts by Air Jets).

Calcination Temperature—The term “calcination temperature” refers to themaximum temperature utilized as an intermediate step in the catalystsynthesis procedure intended to convert the metal salts to their oxideform.

Conversion—The term “conversion of a reactant” refers to the reactantmole or mass change between a material flowing into a reactor and amaterial flowing out of the reactor divided by the moles or mass ofreactant in the material flowing into the reactor. For propanedehydrogenation, selectivity is the mass of propane reacted divided bythe mass of propane fed.

“Particle size” is number average particle size, and, for non-sphericalparticles, is based on the largest dimension.

Pore size—Pore size relates to the size of a molecule or atom that canpenetrate into the pores of a material. As used herein, the term “poresize” for zeolites and similar catalyst compositions refers to theNorman radii adjusted pore size well known to those skilled in the art.Determination of Norman radii adjusted pore size is described, forexample, in Cook, M.; Conner, W. C., “How big are the pores ofzeolites?” Proceedings of the International Zeolite Conference, 12th,Baltimore, Jul. 5-10, 1998; (1999), 1, pp 409-414.

One of ordinary skill in the art will understand how to determine thepore size (e.g., minimum pore size, average of minimum pore sizes) in acatalyst. For example, x-ray diffraction (XRD) can be used to determineatomic coordinates. XRD techniques for the determination of pore sizeare described, for example, in Pecharsky, V. K. et at, “Fundamentals ofPowder Diffraction and Structural Characterization of Materials,”Springer Science+Business Media, Inc., New York, 2005. Other techniquesthat may be useful in determining pore sizes (e.g., zeolite pore sizes)include, for example, helium pycnometry or low-pressure argon adsorptiontechniques. These and other techniques are described in Magee, J. S. etat, “Fluid Catalytic Cracking: Science and Technology,” ElsevierPublishing Company, Jul. 1, 1993, pp. 185-195. Pore sizes of mesoporouscatalysts may be determined using, for example, nitrogen adsorptiontechniques, as described in Gregg, S. J. at al, “Adsorption, SurfaceArea and Porosity,” 2nd Ed., Academic Press Inc., New York, 1982 andRouquerol, F. et al, “Adsorption by powders and porous materials.Principles, Methodology and Applications,” Academic Press Inc., NewYork, 1998.

Regeneration Temperature—The catalyst may be regenerated under flowingair gas at elevated temperatures in order to remove heavier hydrocarbons(coke) from the active catalyst structure. The maximum temperature usedin this step is referred to as the “regeneration temperature.”

Residence Time (τ)—Residence time is the time a substance is in thereaction vessel. It can be defined as the volume of the catalyst beddivided by the flow rate (by volume per second) of gases into thereactor. r=volume of Catalyst bed (m³)/volumetric flow of reactants(m³/s).

Selectivity—The term “selectivity” refers to the amount of production ofa particular product (or products) as a percent of all productsresulting from a reaction. For example, if 100 grams of products areproduced in a reaction and 80 grams of olefins are found in theseproducts, the selectivity to olefins amongst all products is 80/100=80%.Selectivity can be calculated on a mass basis, as in the aforementionedexample, or it can be calculated on a molar basis, where the selectivityis calculated by dividing the moles a particular product by the moles ofall products. Unless specified otherwise, selectivity is on a massbasis. For propane dehydrogenation, selectivity is the mass of propyleneproduced divided by the mass of all products.

Yield—The term “yield” is used herein to refer to the amount of aproduct flowing out of a reactor divided by the amount of reactantflowing into the reactor, usually expressed as a percentage or fraction.Mass yield is the mass of a particular product divided by the weight offeed used to prepare that product. When unspecified, “%” refers to mass% which is synonymous with weight %. Ideal gas behavior is assumed sothat mole % is the same as volume % in the gas phase. For propanedehydrogenation, mass yield is the mass of propylene produced divided bythe mass of propane fed. Mass yield of the inventive processes arepreferably at least 50% in a single pass, preferably at least 70%.

As is standard patent terminology, the term “comprising” means“including” and does not exclude additional components. Any of theinventive aspects described in conjunction with the term “comprising”also include narrower embodiments in which the term “comprising” isreplaced by the narrower terms “consisting essentially of” or“consisting of.” As used in this specification, the terms “includes” or“including” should not be read as limiting the invention but, rather,listing exemplary components. As is standard terminology, “systems”include to apparatus and materials (such as reactants and products) andconditions within the apparatus.

DETAILED DESCRIPTION

The catalyst can be used as powder or pellet, or can be disposed on asubstrate such as a reactor wall or on beads or other support. Forexample, the catalyst can be deposited on a silica powder. This issometimes termed as a catalyst material “grafted” on a support.

The catalyst preferably comprises a stabilized titania support.Preferably, the titanium in the catalyst is chiefly in the form ofanatase as determined by XRD. Typically, the catalyst (not including anoptional support material) comprises from 10 to 95 wt % titania,preferably 50 to 95, or 70 to 95, or 80 to 93 wt % titania (calculatedassuming all Ti is present as TiO2).

The titania is stabilized with a stabilizing element comprisingzirconium, tungsten, or a rare earth element or combinations thereof.The rare earth element, if present, preferably includes Ce and/or Y. Thestabilizing element(s) are preferably present in 0.1 to 25 wt % (basedon the weight of the fully oxidized, oxide form of the stabilizerelement, or 0.1 to 20 wt %, or 0.5 to 20, or 1.0 to 20, or 0.5 to 15, or0.5 to 10, or 1.0 to 15, or 2.0 to 15, or 2.0 to 10, or 4.0 to 8.0 wt %(based on the elements weight).

The catalyst preferably contains zinc, preferably in the range of 0.1 to10%, more preferably 1 to 10, or 2 to 8, or 3 to 7 wt %.

Preferably, the catalyst comprises a BET surface area of at least 1, orat least 5, or at least 20, or in the range of 1 to 50, or 1 to 35 m²/g.

The invention includes methods of making the catalyst, methods ofdehydrogenating a paraffin having 2-8 carbon atoms (preferably propaneor isobutane). The invention also includes reaction systems comprising areactor comprising any of the catalysts described herein, a productstream comprising a paraffin having 2-8 carbon atoms (preferably propaneor isobutane) passing through the reactor and in contact with thecatalyst, preferably at the temperature and rate conditions describedherein.

In a preferred method, the catalyst is employed in the dehydrogenationof a paraffin having 2-8 carbon atoms (preferably propane or isobutane).For example, in some embodiments, the catalyst is exposed to a streamcomprising at least 50 mol % propane. In some embodiments, the method isconducted with a product stream of paraffins at a space velocity of 0.1to 10 hr⁻¹, or 0.5 to 5, or 0.5 to 2 hr⁻¹, and preferably at atemperature of 500 to 700 C. In some embodiments, the method isconducted for a continuous period of at least 1 second or from 1 secondto 120 seconds without regeneration and with a stability such that therate of dehydrogenation decreases by no more than 10% or no more than 5%or no more than 2% over the continuous period.

Surprisingly, we have discovered that a catalyst containing titania andzinc, and stabilized by Zr, W, and/or rare earth metals exhibits asurprisingly superior combination of activity, selectivity, andstability results under conditions of propane dehydrogenation.

The invention is further elucidated in the examples below. In somepreferred embodiments, the invention may be further characterized by anyselected descriptions from the examples, for example, within ±20% (orwithin ±10%) of any of the values in any of the examples, tables orfigures; however, the scope of the present invention, in its broaderaspects, is not intended to be limited by these examples.

EXAMPLE 1

The starting material was titanium (IV) oxide obtained from BASF. Anappropriate amount of Zinc Nitrate Hexahydrate salt was dissolved indeionized water at room temperature to make a 10 wt % Zinc Nitratesolution. This solution was then added dropwise to the titanium (IV)oxide support. The wet catalyst was then left to dry at room temperatureovernight. The catalyst was then calcined in a muffle furnace at 600° C.for 4 hours. The final catalyst had 3 wt % Zinc by weight. This catalystis designated as Catalyst A.

EXAMPLE 2

The catalyst was prepared as in Example 1 using silica (SiO₂) obtainedfrom Sigma Aldrich as the catalyst support. This catalyst is designatedas Catalyst B.

EXAMPLE 3

The catalyst was prepared as in Example 1 using ceria (CeO₂) obtainedfrom Sigma Aldrich as the catalyst support. This catalyst is designatedas Catalyst C.

EXAMPLE 4

The catalyst was prepared as in Example 1 using gamma-alumina (⋅-Al₂O₃)obtained from Alfa Aesar as the catalyst support. This catalyst will bedesignated as Catalyst D.

EXAMPLE 5

Propane dehydrogenation experiments were performed using a fixed-bedreactor such that the d_(T)/d_(P)>10 (ratio of diameter of reactor tubeto diameter of catalyst particles) and L/d_(P)>50 (ratio of length ofcatalyst bed to diameter of catalyst particles) to ensure plug-flowbehavior. The catalyst of interest was first loaded into a quartz glasslined reactor. The catalyst was activated in dry air at atmosphericpressure at a temperature of 600° C. for 4 hours. Following activation,the reactor was allowed to heat up to reaction temperature of 625° C.,then purged with dry nitrogen for 0.5 hours. Propane was fed to thereactor at a WHSV equal to 1 hr⁻¹. The flow rate was controlled by aBrooks mass flow controller. Product samples taken 5 minutes after thestart of reaction were analyzed on GCs having Petrocol DH and Plot Qcolumns. The catalyst was regenerated at 625° C. by first purging thereactor with nitrogen and then passing air over the catalyst. Theresults are shown in Table 1.

TABLE 1 Activity Selectivity Catalyst # Support Parameter Parameter ATiO₂ 1850 0.245 B SiO₂ 272 2.346 C CeO₂ 467 2.331 D γ-Al₂O₃ 2694 1.244

Results show that TiO₂ as the best support for propane dehydrogenation.However, none of these supports showed adequate catalyst stabilityrequired for commercial application.

EXAMPLE 6

The starting material was titanium (IV) oxide obtained from Alfa-Aesar.An appropriate amount of Zinc Nitrate Hexahydrate salt was dissolved indeionized water at room temperature to make a 3 wt % Zinc Nitratesolution. This solution was then added dropwise to the titanium (IV)oxide support. The wet catalyst was then left to dry at room temperatureovernight. The catalyst was then calcined in a muffle furnace at 600° C.for 4 hours. The final catalyst had 1 wt % Zinc by weight. This catalystis designated as Catalyst E.

EXAMPLE 7

The starting material was titanium (IV) oxide obtained from Alfa-Aesar.An appropriate amount of Zinc Nitrate Hexahydrate salt was dissolved indeionized water at room temperature to make a 6 wt % Zinc Nitratesolution. This solution was then added dropwise to the titanium (IV)oxide support. The wet catalyst was then left to dry at room temperatureovernight. The catalyst was then calcined in a muffle furnace at 600° C.for 4 hours. The final catalyst had 2 wt % Zinc by weight.

This catalyst is designated as Catalyst F.

EXAMPLE 8

The starting material was titanium (IV) oxide obtained from Alfa-Aesar.An appropriate amount of Zinc Nitrate Hexahydrate salt was dissolved indeionized water at room temperature to make a 9 wt % Zinc Nitratesolution. This solution was then added dropwise to the titanium (IV)oxide support. The wet catalyst was then left to dry at room temperatureovernight. The catalyst was then calcined in a muffle furnace at 600° C.for 4 hours. The final catalyst had 3 wt % Zinc by weight.

This catalyst is designated as Catalyst G.

EXAMPLE 9

The starting material was titanium (IV) oxide obtained from Alfa-Aesar.An appropriate amount of Zinc Nitrate Hexahydrate salt was dissolved indeionized water at room temperature to make a 12 wt % Zinc Nitratesolution. This solution was then added dropwise to the titanium (IV)oxide support. The wet catalyst was then left to dry at room temperatureovernight. The catalyst was then calcined in a muffle furnace at 600° C.for 4 hours. The final catalyst had 4 wt % Zinc by weight.

This catalyst is designated as Catalyst H.

EXAMPLE 10

Catalysts E, F, G and H were tested for propane dehydrogenation activityas described in Example 5. The results are shown in Table 2.

TABLE 2 Zinc Activity Selectivity Catalyst # Loading Parameter ParameterE 1 wt % 2615 0.912 F 2 wt % 1912 0.216 G 3 wt % 3017 0.194 H 4 wt %5391 2.827

Results shown in Table 2 clearly show that catalyst G with 3 wt % Znloading has desired characteristics of adequate activity andselectivity.

EXAMPLE 11

The catalyst was prepared as in Example 6 with the only difference beingthe doping of the support with 10 wt % Cerium prior to addition of zincnitrate. Titanium oxide support was doped with 10% Cerium as follows: A10 wt % cerium nitrate hexahydrate aqueous solution was first addeddropwise to the titanium oxide support. The wet catalyst was then leftto dry at room temperature overnight and then calcined to 600° C. for 4hours. The addition of Zinc to the resulting support was then followedas in example 1.

This catalyst is designated as Catalyst I.

EXAMPLE 12

The catalyst was prepared as in Example 11 with the only differencebeing the titanium oxide support was doped with 10 wt % Lanthanum.

This catalyst will be designated as Catalyst J.

EXAMPLE 13

The catalyst was prepared as in Example 11 with the only differencebeing the titanium oxide support was doped with 10 wt % Yttrium.

This catalyst will be designated as Catalyst K.

EXAMPLE 14

Catalysts I, J and K were tested for propane dehydrogenation activity asdescribed in Example 5. The results are shown in Table 3.

TABLE 3 Catalyst # Rare Earth Activity Parameter Stability Parameter GNone 2939 18.5E−03  I CeO₂ 2752 1.9E−03 J La₂O₃ 2443 7.5E−03 K Y₂O₃ 23293.3E−03

Results shown in Table 3 show the benefit of adding a Rare Earth Oxideto TiO₂ for stabilizing catalyst activity.

EXAMPLE 15

A composite support comprising of Titania, Zirconia and Silica with aTiO₂:ZrO₂:SiO₂ ratio of 18:1:1 by weight was synthesized using a sol-gelhydrolysis technique. The appropriate amounts of Titanium (IV)Iso-propoxide, Zirconium (IV) propoxide and Tetra ethyl orthosilicatewere mixed in 2-Propanol. The mixture was kept stirred using a magneticbar at room temperature. Warm 0.1 M NH₄NO₃ aqueous solution was thenadded to the alkoxide mixture for hydrolysis.

The resulting hydrolyzed sol-gel was allowed to stand at roomtemperature overnight. The sol-gel was dried and calcined at 450° C. for4 hours. 3% Zinc was added to support as described in Example 1. Thiscatalyst will be designated as Catalyst L.

EXAMPLE 16

The appropriate amount of Titanium Isopropoxide, Zirconia and Silicawith a TiO₂:ZrO₂:SiO₂ ratio of 18:1:1 by weight were mixed in2-Propanol. Silica gel (150 Angstrom pore size) was slowly poured intothe solution. The slurry mixture was stirred for 24 hours at roomtemperature. At the end of 24 hours, the mixture was heated at 70° C.for 1 hour. After 1 hour of heating, the excess solvent was decanted andresidual solvent was driven off under the vacuum. The grafted supportwas hydrolyzed at 40° C. overnight. The hydrolyzed support was calcinedto a temperature of 550° C. for 4 hours. The final loading of TiO₂ onthe silica support was 10 wt %. 3 wt % Zinc as an active metal was addedto grafted support employing a wet impregnation technique as describedin Example 1. This catalyst will be designated as Catalyst M.

EXAMPLE 17

Catalysts L and M. were tested for propane dehydrogenation activity asdescribed in Example 5. The results are shown in Table 4.

TABLE 4 Activity Selectivity Catalyst # Parameter Parameter L 3017 0.194M 2926 0.204

As evident from table 4, the performance of the hydrolyzed catalyst andthe grafted catalyst are essentially the same despite the fact that thegrafted catalyst contains>88% of inert material.

EXAMPLE 18

24 gm of Titanium Tetrachloride and 1.7 gm of Zirconium Tetrachloridewere dissolved in 500 ml of deionized chilled (5° C.) water. Thesolution was heated to 55° C. while stirring. When the desiredtemperature was reached, 2 molar aqueous solution of ammonium hydroxidewas added to solution till it reached a pH of 7.3. The precipitate wasfiltered and dried overnight and then calcined to a temperature of 700°C. for 4 hours to produce the stabilized catalyst support. 0.34 gm ofZinc Nitrate Hexahydrate was dissolved in 2.5 grams of deionized waterat room temperature. The solution was then added to 11 grams of thestabilized catalyst support dropwise. The wet catalyst was dried andcalcined at 700° C. for 4 hours to give a Zn loading of 3 wt %.

This catalyst is designated as Catalyst N.

EXAMPLE 19

2.6 gm of Zinc Nitrate Hexahydrate, 24 gm of Titanium Tetrachloride and1.7 gm of Zirconium Tetrachloride inorganic salts were dissolved in 500ml of deionized chilled (5° C.) water. The solution was heated to 55° C.while stirring. When the desired temperature was reached, 2 M aqueoussolution of ammonium hydroxide was added to the inorganic salts solutiondropwise until the solution reached a pH of 7.3. The precipitate wasfiltered and dried overnight and then calcined to a temperature of 700°C. for 4 hours to produce the mixed-metal oxide catalyst This catalystis designated as Catalyst O.

EXAMPLE 20

The catalyst was prepared as in Example 19 with the only differencebeing the amount of Zinc Nitrate Hexahydrate added was 1.3 gm.

This catalyst is designated as Catalyst P.

EXAMPLE 21

The catalyst was prepared as in Example 19 with the only differencebeing the amount of Zinc Nitrate Hexahydrate added was 4.0 gm.

This catalyst is designated as Catalyst Q.

EXAMPLE 22

The catalyst was prepared as in Example 19 with the only differencebeing the amount of Zinc Nitrate Hexahydrate added was 5.5 gm.

This catalyst is designated as Catalyst R.

EXAMPLE 23

The catalyst was prepared as in Example 19 with the only differencebeing the amount of Zinc Nitrate Hexahydrate added was 8.8 gm.

This catalyst is designated as Catalyst S.

Catalysts J to N were tested for propane dehydrogenation followingExample 5 with the only difference being the propane WHSV was 2/hr. Theresults are shown in the Table 5.

TABLE 5 Zinc Loading Activity Selectivity Stability Catalyst (wt %)Parameter Parameter Parameter O  5% 28864.2 0.19 0 P 2.5%  27930.21 0.41Not measured Q 7.5%  21791.86 0.49 Not measured R 10% 27011.41 0.44 Notmeasured S 15% 14768.42 1.05 Not measured

The results show that excessive Zn loading can lead to inferior catalystperformance.

EXAMPLE 24

2.6 gm of Zinc Nitrate Hexahydrate, 22 gm of Titanium Oxy-Sulfate and1.7 gm of Zirconium Tetrachloride inorganic salts were dissolved in 500ml of deionized water. The salt solution was heated to 55° C. whilestirring. When the desired temperature was reached, 2 molar aqueoussolution of ammonium hydroxide was added to the inorganic salts solutiondropwise till the precipitate reached the pH of 7.3. The precipitate wasfiltered and dried overnight and then calcined to a temperature of 700°C. for 4 hours to produce the mixed-metal oxide catalyst. This catalystis designated as Catalyst T.

EXAMPLE 25

The catalyst was prepared as in Example 24 with the only differencebeing amount of Zinc Nitrate Hexahydrate added was 1.3 gm. This catalystis designated as Catalyst U.

EXAMPLE 26

The catalyst was prepared as in Example 24 with the only differencebeing amount of Zinc Nitrate Hexahydrate added was 4.0 gm. This catalystis designated as Catalyst V.

EXAMPLE 27

The catalyst was prepared as in Example 24 with the only differencebeing amount of Zinc Nitrate Hexahydrate added was 5.5 gm. This catalystis designated as Catalyst W.

EXAMPLE 28

The catalyst was prepared as in Example 24 with the only differencebeing amount of Zinc Nitrate Hexahydrate added was 8.8 gm. This catalystis designated as Catalyst X.

EXAMPLE 29

The catalyst was prepared as in Example 24 with the only differencebeing the bulk catalyst was washed with dilute NH₄OH solution followedby dilute NH₄NO₃ solution for 30 minutes at room temperature. Thiscatalyst is designated as Catalyst AI. The catalyst was submitted forBET analysis.

Catalysts T, U, W and AI were tested for propane dehydrogenationfollowing Example 5 with the only difference being the propane WHSV was2/hr. The results are shown in Table 6.

TABLE 6 Zinc Loading Activity Selectivity Catalyst (wt %) ParameterParameter T  5% 25217.45 0.5 U 2.5%  19352.41 0.4 W 10% 5329.02 13.71 AI33 32762.64 0.15

The results indicate that washing the precipitate with ammonium nitrateand ammonium hydroxide solutions significantly improve catalystperformance.

EXAMPLE 30

2.4 gm of Zinc Nitrate Hexahydrate and 22 gm of Titanium Oxy-Sulfateinorganic salts were dissolved in 500 ml of deionized water. The saltsolution was heated to 55° C. while stirring. When the desiredtemperature was reached, 2 molar aqueous solution of ammonium hydroxidewas added to the inorganic salts solution dropwise till the precipitatereached the pH of 7.3. The precipitate was filtered, washed with 0.1 MNH₄OH for 30 minutes at room temperature followed by 0.25 M NH₄NO₃ washfor 30 minutes at room temperature. The catalyst was dried overnight andthen calcined to a temperature of 700° C. for 4 hours to produce themixed-metal oxide catalyst. This catalyst is designated as Catalyst AJ.The catalyst was submitted for BET analysis

EXAMPLE 31

Commercially available Zinc Orthotitanate (ZnO.TiO₂) was obtained fromAlfa Aesar. The catalyst was activated in situ at 450° C. overnight. Thecatalyst was tested for propane dehydrogenation reaction followingsimilar operating condition as tested for other in-home synthesizedcatalysts. This catalyst is designated as Catalyst AK. The catalyst wassubmitted for BET analysis.

EXAMPLE 32

The starting material was Tungsten (5 wt % WO₃) stabilized titanium (IV)oxide obtained from Cristal. An appropriate amount of Zinc NitrateHexahydrate salt was dissolved in deionized water at room temperature tomake a 10 wt % Zinc Nitrate solution. This solution was then addeddropwise to the titanium (IV) oxide support. The wet catalyst was thenleft to dry at room temperature overnight. The catalyst was thencalcined in a muffle furnace at 700° C. for 4 hours. The final catalysthad 3 wt % Zinc by weight. This catalyst is designated as Catalyst AL.

Catalysts AJ to AL were tested for propane dehydrogenation followingExample 5 with the only difference being the propane WHSV was 2/hr. Theresults are shown in the table 7. below:

TABLE 7 BET surface Activity Selectivity Catalyst area (m²/gm) Parameterparameter AJ 8 14768.42 0.68 AK <1 1721.1 28.52 AL 87.2 35028 0.25

The data shows that the surface areas of TiO₂ supports dropsignificantly when raised to temperatures in excess of 600° C. withoutthe presence of stabilizers such as WO₃ or ZrO₂.

EXAMPLE 33

Sample AI was submitted for XRD analysis to determine the crystallinephases present. Results are shown in FIG. 2. Based on comparison withTiO₂ samples, the results show the presence of anatase phase as themajor component in sample AI.

EXAMPLE 34

Sample AI was submitted for XRD analysis to determine the crystallinephases present. Results are shown in FIG. 3. Based on XRD comparisonwith Zinc-Titanate samples, the results show the presence of ZnO-TiO₂ asthe major component in sample AK.

The XRD data show the presence of anatase phase for the ZrO2 doped TiO2support while the commercial ZnO.TiO₂ shows clearly the presence of ZincTitanate Phase.

1-33. (canceled)
 34. A process for continuous dehydrogenating ofparaffins having 2-8 carbon atoms, preferably propane or isobutane,comprising: contacting said paraffins with a catalyst composition at areaction temperature of 500-800° C., a space velocity of 0.1-5 hr⁻¹ or0.1-1 hr⁻¹ and a pressure of 0.01-0.2 MPa for a reaction period in therange of 0.05 seconds to 10 minutes; regenerating the catalyst with anoxygen-containing gas wherein said catalyst regeneration is performed ata reaction temperature of 500-800° C., a pressure of 0.01-0.2 MPa and aregeneration period ranging from 0.05 seconds to 10 minutes; wherein thecatalyst composition comprises: (a) zinc oxide with optional modifiersselected from the group of Copper, Manganese, and Niobium and astabilized titania support, comprising: the stabilized titania supportstabilized with a stabilizing element(s) comprising zirconium, tungsten,or a rare earth element or combinations thereof; and Zn; wherein thecatalyst composition from 10 to 95 wt % titania, 0.1 to 25 wt % of thestabilizing element(s), 0 to 3 wt % of the modifiers; and 0.1 to 10 wt %Zn; and characterizable by a Activity Parameter>1500, SelectivityParameter<0.2 and a stability parameter<0.005 using a test where themixed metal oxide catalyst is loaded in a fixed-bed reactor such thatthe 50>dT/dP>10 (diameter of tube to diameter of catalyst particles) and200>L/dP>50 (length of catalyst bed to diameter of catalyst particles)and 2>dP>0.5 mm exposed to a feed stream of propane at a temperature of625° C., atmospheric pressure and a feed rate of 2 hr⁻¹ weight hourlyspace velocity; (b) a mixed metal oxide catalyst suitable for thedehydrogenation of paraffins having 2-8 carbon atoms with a catalystcomposition of the general formula (AC) (CS) (ST) wherein AC representsoxides of Transition Metals selected from the group of copper (Cu), iron(Fe), manganese (Mn), niobium (Nb) and zinc (Zn) or mixtures thereof, CSrepresents oxides of aluminum (Al), silicon (Si), and titanium (Ti) ormixtures thereof, ST represents oxides of Rare Earth metals selectedfrom the group of cerium (Ce), dysprosium (Dy), erbium (Er), europium(Eu), gadolinium (Gd), lanthanum (La), neodymium (Nd), praseodymium(Pr), samarium (Sm), terbium (Tb), ytterbium (Yb), yttrium (Y), tungsten(W), zirconium (Zr), or mixtures thereof, and characterizable by aActivity Parameter>1500, Selectivity Parameter<0.2 and a stabilityparameter<0.005 measured using a test where the mixed metal oxidecatalyst is loaded in a fixed-bed reactor such that the 50>dT/dP>10(diameter of tube to diameter of catalyst particles) and 200>L/dP>50(length of catalyst bed to diameter of catalyst particles) and 2>dP>0.5mm exposed to a feed stream of propane at a temperature of 625° C.,atmospheric pressure and a feed rate of 1 hr⁻¹ weight hourly spacevelocity; or (c) a mixed metal oxide catalyst, comprising a catalystcomposition of the general formula (AC) (CS) (ST) (MS) wherein AC(Active Catalyst) represents oxides of Transition Metals selected fromthe group of copper (Cu), iron (Fe), manganese (Mn), niobium (Nb) andzinc (Zn) or mixtures thereof, CS (Catalyst Support) represents oxidesof aluminum (Al), silicon (Si), and titanium (Ti) or mixtures thereof,ST (Support Stabilizer) represents oxides of metals selected from thegroup of cerium (Ce), dysprosium (Dy), erbium (Er), europium (Eu),gadolinium (Gd), lanthanum (La), neodymium (Nd), praseodymium (Pr),samarium (Sm), terbium (Tb), ytterbium (Yb), yttrium (Y) tungsten (W)and zirconium (Zr) or mixtures thereof, MS (Mechanical Stabilizer)represents porous spheres selected from the group of alumina, silica,titania, zirconia, kaolin, meta-kaolin, bentonite, attapulgite, ormixtures thereof; and characterizable by a Activity Parameter>1500,Selectivity Parameter<0.5 and a stability parameter<0.005 using a testwhere the mixed metal oxide catalyst is loaded in a fixed-bed reactorsuch that the 50>dT/dP>10 (diameter of tube to diameter of catalystparticles) and 200>L/dP>50 (length of catalyst bed to diameter ofcatalyst particles) and 2>dP>0.5 mm exposed to a feed stream of propaneat a temperature of 625° C., atmospheric pressure and a feed rate of 2hr⁻¹ weight hourly space velocity.
 35. The process of claim 34, whereinsaid catalyst composition has less than 100 ppm by weight of eitherplatinum (Pt) or chromium (Cr).
 36. The process of claim 34 wherein thecatalyst composition has a BET surface area >30 m²/g.
 37. The process ofclaim 34 wherein the number average particle size of the catalystcomposition is in the range of 30-3000 microns.
 38. The process of claim34 wherein the Air Jet Index of the catalyst composition is less than 10or less than
 5. 39. The process of claim 34 wherein the AC (activecatalyst) species of the catalyst composition makes up 0.1 to 20 wt % ofthe total weight of the catalyst, where weight includes the transitionmetals and associated oxygen needed to balance the oxidation state ofthe transition metals.
 40. The process of claim 34 wherein the activecatalyst species makes up 0.1 to 10 wt % of the total weight of thecatalyst.
 41. The process of claim 34 wherein the active catalystspecies makes up 0.1 to 7.5 wt % of the total weight of the catalyst.42. The process of claim 34 wherein the CS (catalyst support) makes up10 to 95 wt % of the total weight of the catalyst composition.
 43. Theprocess of claim 34 wherein the catalyst support makes up 20 to 90 wt %of the total weight of the catalyst composition.
 44. The process ofclaim 34 wherein the catalyst support makes up 50 to 85 wt % of thetotal weight of the catalyst composition.
 45. The process of claim 34wherein the ST (catalyst stabilizer) makes up 0.1 to 25 wt % of thetotal weight of the catalyst composition.
 46. The process of claim 34wherein the catalyst stabilizer makes up 1 to 15 wt % of the totalweight of the catalyst composition.
 47. The process of claim 34 whereinthe catalyst stabilizer makes up 1 to 10 wt % of the total weight of thecatalyst composition.
 48. The process of claim 34 wherein the catalystsupport comprises a mesoporous bead and wherein the number averageparticle size of the mesoporous bead is in the range of 30-3000 microns.49. The process according to claim 34 wherein the MS (mechanicalstabilizer) species makes up 20 to 85 wt % of the total weight of thecatalyst.
 50. The process of claim 34 wherein said contacting is carriedout in a fluidized bed reactor or a fixed-bed swing reactor.